Teleprinter signal transmission employing a securing code



Dec. 18, 1962 F. Hr-:NNIG Y 3,069,497

TELEPRINTER SIGNAL TRANSMISSION EMPLOYING A SECURING CODE 72,06 #alarm/Wer Dec. 18, 1962 F. HENNIG 3,069,497

TELEPRINTER SIGNAL TRANSMISSION EMPLOYING A SECURING CODE Filed Dec. 19, 1960 2 Sheets-Sheet 2 K d e RQ b DT DT DT DT DT ZDTDTDTDTDTSA United States @attent @dans didllg Patented Dec. l, 1962 3,069,497 TELEPRENTER SIGNAL rtit'tili/SSIN EMPLQY- EN@ A SECURiNtf-,

Fritz Hennig, Munich-Sellin, Gerniany, assigner to Siemens iz Haiske Aktiengeselischaft Bertin and leiiunich,

a German corporation Filed Dee. i9, 195%, Ser. No. 76,718 (ft. 17g-e9) This invention relates to teleprinter symbol transmission and is particularly concerned with telepriuter transmission, especially wireless transmission, of teleprinter symbols, employing a securing code. The present disclosure is a continuation-impart of the co-pending application Serial No. 802,955, tiled March 30, 1959, which is owned by the assignee also named in the present case, now abandoned.

The customary teleprinter code has the well recognized drawback that a completely ditferent symbol (character, numeral, etc.) is produced upon falsication of a single symbol or signal element, and that it cannot be recognized at the receiver whether or not the received symbol actually corresponds to the transmitted symbol. However, the use of a socalled securing code permits, depending upon the kind of code employed and especially upon the number of signal elements for the individual symbols, to indicate and even to correct at the receiver more or less of the disturbance.

A securing code is employed particularly in connection with wireless teleprinier connections which are known for disturbances caused, for example, by interference fields 9 or by fading.

Most varied types of codes have become known as securing codes. One type provides for each individual teleprinter symbol a tixed ratio of space to mark signal elements. The best known code of this type is the socalled 7-element code, in which each individual symbol is composed of three space elements and four mark elements. The fact that an error is present can be ascertained at the receiver by the use of a code testing device in case a symbol is received which does not have this ratio of space to mark elements. This results n a relatively great number of symbols which have to be verified and an automatically operating check-back or verication device is therefore usually provided which effects transmission of a verification signal from the receiver to the transmitter whenever the code testing device recognizes an erroneous symbol. The transmitting station is thus caused to retransmit previously transmitted symbols.

Other securing codes have become known which permit to ascertain at the receiver whether a symbol is erroneous or correct and accordingly, requiring verification or making verification unnecessary.

The invention is concerned with a teleprinter transmission system provided with automatically operating checkback or verication. The system includes a transmitting station for transmitting to a receiving station teleprinter symbols coded in securing code, the receiving station coinprising a code testing device which effects in the presence 0f non-correctible errors transmission of a verification signal to the transmitting station so as to cause the latter to retransmit several of the previously transmited symbols which had been temporarily stored in a storer at the transmitter.

According to the invention, the capacity of such storer permits storing of a plurality of the last transmitted symbols, including the symbol which precedes a disturbed symbol, so that retransmission, responsive to a verification signal starts with such preceding symbol. The advantage resides in considerable reduction of the number of erroneous symbols, since there is great probability that the symbols adjacent to the symbol which the code testing 2 device recognized as being erroneous, are likewise falsified but had been erroneously evaluated by the code testing device, for example, due to transposition errors.

The various objects and features of the present invention will appear from the description which is rendered below with reference to the accompanying drawings, showing a teleprinter symbol transmission system with automatic verification, in which teleprinter symbols are transmitted in two-way operation in opposite directions. The principle of operation of such a transmission system is known, for example, from the US. Patent No. 2,313,980.

FiGS. la and 1b show an example of the system in the case of normal transmission conditions, that is, all switching devices are indicated in the condition in which they are in trouble-free operation; and

FIG. 2 represents in diagrammatic manner salient fea.- tures of the system which are operable in transmitting and receiving symbols.

The operation is as follows:

The punched tape transmitter litt) (station AFltG. la) transmits S-element teleprinter symbols in parallel representation to the code converter lill which effects conversion thereof into the 7-element code. The symbols of the 7-element code are extended from the output of the code converter 101 over the switch 102 to the storer or shift register 103, the storage content of which is stepped along in the rhythm of the individual teleprinter symbols, by timing pulses conducted to the terminal "a which are extended over the switch 169. The storage content present at any instant in the first stage of the storer 103 is extended over the switch 164 to the transmitter distributor '.ti which converts the individual elements of the 7-element symbol into series representation so as to effect transmission over the transmission channel Stili by way of the transmission device itt?. An example of symbols transmitted by the transmitting device MW is shown in line lti' in FIG. 2.

he transmitted symbols are received at the station B (FIG. lb) in the receiver device 229. Such received symbols are represented in line 22d of FIG. 2, the transmission time over the channel 360 being assumed to amount to one half symbol length. The receiver distributor 221 converts the serially incoming elements of each symbol into parallel representation and extends them to the code testing device 222 which examines the symbols as to the correct 3 to 4 ratio, at the same time testing with respect to the presence of a verification signal RQ. A suitable code testing device is described in U.S. Patent No. 2,552,- 126. The symbols are extended from the code testing device 222 to an intermediate storer 223 with a storage capacity corresponding to one symbol. Accordingly, and as will be seen from line 223 of FlG. 2 there is in the intermediate storer 223 stored the symbol which precedes the just received teleprinter symbol. From the intermediate storer 223, the symbols are extended over the switch 224 to the device 225 in which they are converted from the 7-element to the 5-element code and in which they remain stored up to the instant of further transmission. The symbols appearing at the output of the device 0 225 are represented in line 225 in FIG. 2. They are extended for further transmission to the device 226 and to the punched tape receiver 22'7.

Teleprinter symbols are in completely analogous manner transmitted over the channel Stil from the punched tape transmitter 2th) of the station B (FIG. lb) to the punched tape receiver 127 of the station A (FIG. la). The symbols transmitted from the transmitter device 297 of the station B are represented in line of FG. 2. The teleprinter symbols stored in the intermediate storer i2?) of station A are represented in line 123 of FIG. 2. At the output of the device 12S of the station A are obtained the symbols represented in line of FIG. 2.

As will be seen from FlG. 2, line i627, the symbol or character a was correctly transmitted from the transmitting device le? of the station A to the receiving device 22@ ofthe station B. The character b however was due to a transposition error falsied into the character t. This error had not been recognized by the code testing device 222 since the character t likewise exhibits the correct 3 to 4 ratio. The character c has been recognized as falsified by the code testing device owing to the absence of the 3 to 4 ratio, thus producing an error symbol This error symbol effects actuation, under control of the code testing device 222, of a control circuit 23@ Which in turn effects over the control line 23d/l actuation, for the duration of tive symbols, ot the switches 224, 22S and Ztll as wel] as of the device ldd, and over the control line 23d/2 the actuation, for the duration of one symbol, of switches Zilli and 269. rthis is represented in FG. 2 in lines 23d/.l and 23%/ 2. Since the switch 22d is open, the symbols will not be extended from the intermediate storer 223 to the device The switch 228 is at the same time closed and, accordingly, a device 229 is connected to the device 225. The device 229 is effective to produce at the output of the device prolonged space polarity DT as is represented in line 225 of FIG. 2. The switch 262 is at the same time actuated, whereby the output of the stage lV of the storer 203 is connected with the input of the stage l of such storer. The device 2% prevents further reading of symbols From the punched tape transmitter 26?. rl`he switch 26d is moreover opened, thereby extending a shift pulse `for the storer 263. The device 2de is over the actuated switch 204 connected to the transmitter distributor 2il5 for the duration of one symbol. rThe device 2% produces the check-back or verification signal RQ which is now transmitted over the transmitting device 2597 and channel 3;@1 to the station A (FIG. la). See PIG. 2, lines Zil' and The code testing device 122 of station A (EEG. lo) recognizes the RQ-verirlcation signal, thereby effecting actuation of the control device lntl. The switches i215, 128 and 162 as well as the device are now actuated, for the duration of live symbols, over the control line 1.30/1, and the switches ldd and lll@ are actuated, for the duration oi one symbol, over the control line 1361/ 2, such actuation being represented in lines i3d/i and i355/ 2 in FIG. 2.

Since the switch 124 is open, no more symbols are extended from the intermediate storer .23l to the device 125. The device 129 is at the same time connected to the device 125 over the closed switc 8. rllhe device i2@ is effective to produce at the output of the device 125 prolonged space current DT which is extended to the transmission device lo and the punched tape receiver 127. This is represented in line i225 of lFlG. 2. The switch 162 is in alternate actuated position and the output of the stage lV 01' the storer 1d?) is accordingly connected `with the input of stage l. The device ldd is operative to prevent yfurther reading-out of symbols from the punched tape transmitter ldd. Since the switch is opened `for the duration of one symbol, the storer will receive one shift impulse less. The device lilo is at the same time connected to the transmitter distributor tlS over the actuated switch idd. The RQ-veriiication signal is produced in the device ido and is transmitted to the station B (FlG. lb) over the transmitter device lo? and the transmission channel 3%. This is represented in line M7 of HG. 2. The verification or repetition cycle is thus initiated at the station A (FlG. la). The switches iti-fi and i639 are restored to normal by control over the control line i3d/2 after the RQ signal has been transmitted. The content of the storage stage lV of the storer M3 is now transferred over vswitch N52 to the stage l, such operation being eiiected responsive to the next timing pulse which is extended over the switc As will be seen from the drawings, the symbol b is now transmitted rom the stage l of `the storer im over tue switch `ity-",

transmitter distributor 95, the transmission device 107 and channel Sdi), followed by the transmission of the symbols c--d-e7 which had been stored in the stages lll, ll and l of the storer 193. The repetition or verification cycle is now completed. The switches 102, i241, E723 and the device 19S are restored to normal and the symbol transmission is resumed.

At the station B (FIG. lb) and upon expiration of a predetermined time interval, the switches 224, 223 and 291 and the device 2%8 are restored by control over the control line 23d/1, while the switches 264 and 269 are restored by control over the control line 2310/2. As will be seen from the drawings and particularly from line 225 of FIG. 2, the verication also includes repetition of the symbol b which precedes the disturbed symbol c. The operation in the opposite communication direction is analogous, that is, in the transmission from the station B to the station A, the symbol 3 preceding the signal RQ is also repeated. See also line 325 in FIG. 2.

Accordingly, as compared with known systems operating with automatic verication, the `storer of the transmitting station (w3, 2%) must be adapted to store irr each case one more symbol. Moreover, an intermediate storer (223, i214) is required at tie receiving station, which is adapted to always store one symbol. The remaining structure of the system can remain substantially unaltered.

lt is ofcourse understood that the invention is applicable in connection with other codes, for example, a lil-element code, as well as in connection with time multiplex systems operating with automatic verification. lt is likewise understood that given functions, for example, the transmission of a check-back or verification signal, responsive to receipt of a falsied symbol, can be effected manually instead of automatically.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

l claim:

l. A teleprinter symbol transmission system, wherein` telepiinter symbols coded in a securing code are transv mitted from a transmitting to a receiving station, and wherein the receiving station is provided with a code testing device which effects, responsive to recognition; of non-correctible errors, transmission of a vericatonl signal to the transmitting station for the purpose of causing the transmitting station to retransmit previously transmitted symbols which had been stored temporarily in a storer, the improvement which comprises means der always storing in said storer in the course of transmission a plurality of last transmitted teleprinter symbols including the symbol preceding the one which had been recognized as disturbed and the repetition of which is signalled by the verification signal, and means for thereupon effecting retransmission including retransmission of such preceding symbol followed by retransmission of the disturbed symbol.

2. A teleprinter symbol transmission system according to claim l, comprising at the receiving station an intermediate storer electrically connected to the output o the code' testing device, means for storing in said intermediate storer the symbol preceding a symbol which is being' received, symbol evaluation means and receiver recording means connected with the output of said intermediate storer, and means responsive to recognition of a disturbed symbol by said code testing device for interrupting the extension symbols from the intermediate storer for duration of symbol repetition.

3. A teleprinter symbol transmission system according to claim 2, including two teleprinter stations connected for two-way communication, wherein each station is pro-` vided with a code testing device and with a storer as weil as with an intermediate storer as specied.

4. A teleprinter symbol transmission system comprising two stations and channel means for interconnecting se l 5 stations afor two-way communication, each station having means for transmitting to the other station teleprinter symbols coded in securing code and means for receiving and evaluating symbols received from the other station, said transmitting means comprising a storer device which is in the course of transmission operabie to always store a plurality of transmitted symbols, said receiving and evaluating means comprising a code testing device, means controlled by said code testing device upon receipt of a disturbed symbol for temporarily storing the last received undisturbed symbol and for interrupting evaluation of further symbols and for transmitting -to the transmitting station a verification signal signifying that the symbol succeeding the last received undisturbed symbol had been disturbed, means operable at the transmitting station responsive to the receipt of said Verification signal for temporarily interrupting further transmission of symbols and for releasing from said storer device symbols stored therein including the disturbed symbol and the symbol preceding the disturbed symbol, said released symbols being retransmitted to the receiving station to effect correction of the disturbed symbol and to verify correctness of the symbol preceding the disturbed symbol, and means for thereafter resuming transmission of symbols from the transmitting to the receiving station and evaluation thereof in the receiving station.

5. A telcprinter symbol transmission system comprising two stations and channel means for interconnecting said stations for two-Way communication, means at each tion for respectively transmitting to the other station teleprinter symbols coded in securing code and for receiving such symbols, means at each station responsive to the receipt of a disturbed symbol for transmitting to the other station a verification signal signifying the receipt of the disturbed symbol, means operative responsive to the transmission of said vertitcation signal for temporarily interrupting transmission of further symbols at the transmitting station and for temporarily storing the last undisturbed symbol received at the receiving station, means at tne transmitting station for thereupon retransmitting to the receiving station the disturbed symbol and the symbol preceding said disturbed symbol, and means at the transmitting station for thereafter resuming 'transmission of symbols and at the receiving station Ifor receiving such symbols.

References Cited in the file of this patent UNETED STATES PATENZTS 2,706,215 Van Duuren Apr. l2, i955 

